1. Field of the Invention
The present invention relates to a servo control apparatus and particularly to a servo control apparatus which realizes accurate positioning with a positioner within a servo drive system.
2. Description of the Prior Art
As an applied version of such servo control apparatus, an apparatus which positions a head which magnetically records information to the recording surface of a magnetic disk and reproduces such information is already known.
For example, the U.S. Pat. No. 4,488,187 entitled "Servo Control Apparatus" is a typical example. In this patent, however, as a positioning means, a first pulse group and a second pulse group are generated as first servo data and second servo data, and the respective pulse groups are counted and stored individually. Accordingly, this example has a problem that the means for obtaining servo control data is complicated, the apparatus structure becomes large in size and more costly.
To eliminate the above-mentioned problem, the applicant of the present invention previously filed on Aug. 10, 1985, the patent application entitled "Servo Control Apparatus". In the latter application, a voltage controlled oscillator and a reversible counter are used to count the relative displacement of the head, and the count is converted by a digital converter to obtain the servo data for head position control.
This method, however, has the disadvantage that since it is difficult to determine the count start time of a reversible counter and thereby the situation of inaccurate counting of servo data pulses may occur.